Old Material, New Use

Around the country, facility managers are solving difficult roofing problems by using polymethyl methacrylate (PMMA) cold, liquid-applied roofing systems. PMMA roofing systems have been successful in Europe and on the East Coast of the United States for several years, but now are seeing increasing use all over the country. The product is capable of performing well under adverse conditions.

PMMA was first developed in 1928 in several laboratories in Europe and later was brought to market by Rohm and Haas Co. in Germany under the brand name Plexiglas. PMMA is a thermoplastic and, in its original form, transparent. It has been used as an alternative to glass in automobiles and aircraft. Today, PMMA has many uses, from soft contact lenses to the drums that Led Zeppelin’s John Bonham favors. PMMA has proved itself to be a problem-solver in the construction industry for more than 30 years. Many roofing specifiers are learning that its characteristics make it suitable for a roofing system.

Resists standing water

PMMA molecules are hydrophobic, which means that the roofing membrane repels water droplets. This makes PMMA particularly suitable for roofs where ponding water would otherwise be a problem. Many flat or near-flat roofs allow water to stand on the surface for long periods of time. Standing water causes accelerated aging and damage of most roofing membranes, and roofing warranties commonly exclude damage caused by standing water.

PMMA roofing systems aren’t subject to such exclusions. Hydrophobicity also makes it a good choice for inverted or green roofing system designs.

While many roofing materials are susceptible to damage caused by chemical contaminants found on some industrial roofs, PMMA membranes resist most acids and aqueous alkalis, aliphatic hydrocarbons and nonpolar solvents. Vegetable and animal fats have little effect on them. This degree of chemical resistance allows PMMA to succeed where other roofing products could fail. It’s important to check with the manufacturer of any roofing system that you plan to install, but it’s likely that PMMA will resist damage from most contaminants you’ll find at your location.

PMMA membranes are extremely tough, resist physical damage and can be used where frequent abuse could occur. These membranes resist both static and dynamic loads. They withstand roof equipment being placed directly on them. If extreme roof traffic or loads, such as vehicles, are expected, an optional heavy-duty wearing course can be applied.

Penetrations are not problems

PMMA roofing systems are particularly well suited for roofs that have many penetrations. Irregularly shaped penetrations like I-beams, H-beams or conduit pose no problem for this liquid-applied product.

Generally, PMMA flashings are installed as a sandwich of polyester fleece reinforcement between two layers of PMMA polymer encapsulation. The PMMA will adhere to most common building materials, including concrete, masonry, metals and plastic. Its quick curing and ease of application provide a very rapid seamless, reinforced, waterproof termination, without the need for counter-flashing.

Year-round application

Most roofing materials can’t be installed at temperatures below 40°F. That severely restricts roofing project scheduling in most parts of the country. In some places, roof work comes to a standstill during winter. But PMMA membranes can be installed in temperatures as low as 23°F.

Many roofing membranes require hours to cure to a fully rainproof condition. Liquid-applied systems can take as long as 12 hours to cure. PMMA’s rapid cure rate allows projects to be completed and made rain-proof quickly. Cured PMMA membranes are dry to the touch and can withstand rain in less than an hour after installation. Traffic can resume almost immediately.

Recovering work

A PMMA roofing membrane can be used for new construction, replacement or re-covering an existing roofing system. Because PMMA is compatible with almost any roofing substrate, it can be used to overlay the existing roofing membrane. It’s compatible with single-ply, modified bitumen and some types of built-up roof. This characteristic reduces the disruption to the occupants and processes in the building and reduces the risk of in-progress leaks. The time necessary to carry out any roofing project is reduced considerably when the existing membrane doesn’t need to be removed.

PMMA cold, liquid-applied roofing systems represent a relatively new technology for most U.S. facility managers. However, this material has nearly 30 years of successful service in other parts of the world.

Several domestic manufacturers are now producing it, which increases its availability in the United States. These producers express confidence in the future of PMMA roofing in the form of 25-year warranties on their systems. Its somewhat higher installed cost might preclude it from some roofs, but its ability to solve otherwise difficult problems might make it an obvious choice.